Manufacture of plywood tubing and the like



May 9, 1944. P. R. GOLDMAN MANUFACTURE OF PLYWOOD TUBING AND THE LIKE'Filed Jan. 22. 1945 Patented May9, 1944 MANUFACTURE F PLYWQOD TUBINGAND THE LIKE Paul R. Goldman, Andover, Mass., assignor to PlymoldCorporation, Lawrence, Mass., a body corporate Application January 22,1943, Serial No. 473,212

7 Claims.

My present invention relates to the production of hollow tubulararticles such as pipes, tubing and the like of plural-ply material,especially wood veneer or plywood, either alone or in combination withother sheet or strip elements. In a prior copending application SerialNo. 453,931 I disclose and claim lamillar veneer tubing illustrative ofthe product suchv as here concerned, together with methods of making thesame. The present invention aims to improve in certain respects overthat of said earlier application.

AIn the accompanying drawing illustrating diagrammatically the severalsteps or operative phases according to the method of the presentinvention, together with the associated means and product; N

Fig. 1 shows the series of operative stations and apparatus thereat;

Fig. 2 shows in cross-section an initial or core element of the tubing;and

Figs. 3 and 4, on -a somewhat smaller scale, are cross-sectionsrepresenting the tubing as at a second or intermediate stage and a,succeeding or third stage, respectively.

The present method or process as awhole comprises a plurality ofsuccessive operative phases or stages of which three are indicated inthe Fig. l diagram of A, B and C, each including certain steps andstations to be described.

At the iirst station A1 of phase A the inner or core elements 1, seealso Fig. 2, are formed by spirally winding about a mandrel M thin woodstripping or veneer tape 8, 8a, etc., in successive layers or laminae,each with its edges abutting and with each succeeding spiral wrap havingthe opposite hand or direction of wind from the one preceding. In theseveneer strips or tapes, usually about three to seven, and of which veare here represented at 8 to 8d, Fig. 2, as average, the grain orprominent libre direction desirably is lengthwise of the strips, as inmy above identied application.

The mandrel M at this lrst winding station A1 has a diameter the same asor substantially that desired for the inside diameter of the core and ofthe resulting .tube or pipe as a whole, such mandrel being of anadjustable-size type or otherwise, as preferred. The several plies orlaminae of the cores l as formed at station A1 have applied to them abonding or uniting agent,

Apreferably of the polymerizing `or plastic type,

such as a urea formaldehyde, a phenolic resin or 'other composition thepolymerizing or setting of which may be facilitated and expedited by thethe addition of heat. The procedure as described to this point, that is,through station A1 of phase A of Fig. 1, may be the same as orsubstantially that of my mst-mentioned application Serial No. 453,931 tothe corresponding intermediate product status. s

On completion of the winding and the application of the bonding agenteach resulting core l is transferred from a station A1 to a polymerizingor curing station A, Fig. 1. While in Fig. l I have represented but onestation A1 feeding to the station A2, it should be understood that anumber of such stations A1 with their corresponding spiral winding andbonding applying apparatus may be and preferably are employedsimultaneouslyy so that a corresponding number of cores 'l may be underpreparation at any given time.

Following the wrapping of the outermost layers such as 8d, Fig. 2, eachcore 1 is removed from its mandrel M. Each core isthen hermeticallycapped, plugged or otherwise sealed at its two ends, including the endfaces of the pluralply walls themselves and also their central openings,making each core in eiect a closed cylindrical chamber. This sealing maybe done either at station A1 or Az or intermediately. The sever-al coresl as represented at station A2 have received such capping or end sealingmeans, as indicated at la and lb. Further, the cap, plug or like sealingdevice at one end of each core, herein that at 1b, is equipped with aexible or other tubing 'lc 'communicating with the closed interior ofthe core and adapted for introducing thereto a gaseous medium, such asair, under pressure and desirably in a heated condition. l

At the core treating station A2 of phase A of the process one or anyconvenient plurality of the cores l are vertically or otherwisesupported as upon an appropriate rack or frame or by sus'- pending them,as from an overhead track or endless conveyer, either by the gas in letV,tubing lc itself or other suspension means. This tubing 'lc for eachcore is in communication with a source of supply 0f the air or othergaseous medium under pressure, such as an air compressor of appropriatecapacity, desirably adapted to afford pressures up to about lbs. as theapproximate maximum. Where the medium is air, and also in the-case ofother adequately stable gaseous media, these may be heated totemperatures ranging from room temperature up to as high as 300 F. ormore, in some instances, depending on the particular bonding agentemployed. The core elements l from the station or staapplication ofpressure, either with or without Il tions A1 in their initial gre'en ornon-polymen'zed condition are` to an appreciable extent permeable orpenetrable by the compressed air or other gaseous medium at the positivepressure differentials contemplated. The resistance to permeativepassage of the pressure medium through the cylindrical wall of a corevaries somewhat with the gauge of the veneer, the kind of wood, thenumber of veneer plies contained and the nature of the bonding agent. Insome instances it is found desirable to retard the through passage ofthe gasby applying to the cores a temporary outside sheath such as apaper wrap or a light coating of removable quick-drying lacquer or othersealing agent. In the great majority of cases, 'however,'such externaltreatment is found unnecessary, the permeation of the air or other gasunder pressure through the cylindrical walls of the cores usually beingat such a slow rate that the desired positive pressure differential asbetween the inside and outside of the core and internally of andthroughout the core walls is of itself is concerned, it may besubstantially the same as fully described in connection with Figs. 4 and5 of my said copending case. As there explained, the straight-woundveneer sheeting element l0 may comprise one or a plurality of full turnsor wraps, with the leading and the terminal longitudinal edges in closeradial proximity to each other, so that the entire resultingcore-surrounding element I0 is of uniform thickness free of excessoverlap or part turns, and regardless of the gauge of the veneer whichgenerally is of the ordei of V54 to 1/100 in. for tubing of from about1/4 in. up to 3 or 4 in. internal diameter.

Before or during winding of the core-surrounding readily maintained forthe necessary pOlymerizing period at the station A2.

The gaseous pressure differential thus supplied internally of the cores,and also the temperature, where heat above room temperature is employed,are proportioned-as appropriate to the particular urea formaldehyde,phenolic or other bonding agent and to the character and total thicknessof the cylindrical wall of the given core. Largely by reason of thepermeative action and penetration of the gas pressure medium into andthrough the core walls, whereby such medium and its positive pressuredifferential is more or less directly effective upon the bonding agentwithin the walls, the curing and polymerizing period is materiallyshortened. Thus the duration of the internal pressure and heat treatmentas at station A2 may in many cases be as brief as 10 minutes or evenless, and for the least readily pressurepermeable cores seldom requiresmore than one or a few hours. In general, the greater the positivepressure differential applied, the less is the time required. Also thetime period in general may be shortened by heat, whatever the internalpositive pressure differential utilized.

At. the end of this permeative gas pressure period'the first main phaseor step A of the process is completed, the various cores 1 then being inreadiness for transfer from station A2 for storage or furtherprocessing. These polymerized hard dry cores 1 may proceed from stationA2 by endless conveyor or other transfer, to a second main operativephase B, which also comprises two steps and stations as indicated at B1and B.

At a station such as B1 the base tubes or cores 1 are themselvesmanipulated in the manner of mandrels, each to have wrapped about it alongitudinally rigidifying element represented as a whole by the numeralIll.` The resultant intermediate tubular structure comprising the base 1and the surrounding element l0 will be referred to as the tubing body.

Similarly as in my preceding application Serial No. 453,931, thecore-surrounding element I0 comprises one or more wraps of wood veneerin sheet form wound straight onto the-given core 1, that is, with theside edges of the single or plural ply veneer sheets perpendicular tothe core axis. These veneer sheets are selected and a1"- ranged to havethe grain or fibre extend predominantly crosswise the'sheet and hence inor approximately in parallelism with the axis of the core as the veneeris wo d onto th'e latter.

element l0 of station B1, it is coated at one or both faces, except atthe externally exposed surface of the ilnal wrap, with a similarimpregnating and bonding agent as in connection with the formation ofthe core 1.

As in the case of phase A, there may be a plurality of stations B1simultaneously operating upon a like number of cores 1 to apply to themthe straight-wound veneer elements ill. On completing said winding atthe one or more stations Bl the resulting tube bodies, each comprising acore 1 plus an intermediate straight-on veneer winding I0, aretransferred by conveyor or otherwise to station B2.

At or before reaching station B2 the tube bodies 1-l0 are capped,plugged or otherwise endsealed, similarly as in preparation for theprevious core treatment at station A2, it being understood that if anyportion of such prior sealing means overlapped the end portion of. theouter cylindrical wall of the core, in the manner of a flanged cap, atleast such portion is removed prior to the winding on of theintermediate element I0. Otherwise the same sealing means may beretained from station A2 through the succeeding phases B and C, save forany appreciable projecting length of the pressure and heating tubingsuch as 1b.

l At station B2 one-'or more of the tube bodies 1-l0 are suspended orotherwise supported or conveyed in a generally similar manner as inconnection with station A2. Here, however, the tube bodies are placed inor caused to travel through a closed pressure-tight chamber, asdesignated by the full line enclosureb. And in this case the exibletubing or the like 1b, instead of receiving a positive pressure mediumis maintained in open communication with atmosphere or is connected to asource of negative pressure (vacuum), thereby to facilitate the creatingof a positive pressure differential externally of, upon and into orthrough the body walls, as contrasted with the previous inside-outpressure as at station A2.

The tube bodies 1-I0 in the pressure-tight chamber b are externallysubjected to a gaseous medium, generally air, under substantialpressure. This may be accomplished by pumping the air or other gasmedium into, or admitting it under the selected pressure, to the chamberb. as at the pressure entrance port bx. By keeping the sealed hollowinteriors of the tube bodies in communication with atmosphere throughthe described tubing connections or similarly creating a negative orless-than-atmospheric pressure In so far as the proce ure at station B1in and 75 within them, the desired positive external pressuredifferential is attained. The procedure at station B2 may be expedited,with economy in supplying of the pressure medium, by the' provision ofair-locks in connection with the chamber b, the tube bodies entering andleaving the lthe presence of the supporting chamber through suchpressure-conserving locks..

Since the tubebodies 1I 0 to be compressively treated at station B2 havethe composite strength of both the spiral-wound core element 'I and thestraight-on applied veneer winding I0, a higher range of pressuredifferentials generally may be employed than at the core treatingstationA2. Thus for example the positive pressuredifferentials employedinternally of the cores 'las at station A2 generally is within a rangeof about 15 to 50 lbs., while at station B2, by reason of radially rigidcores, external pressure differentials of a substantially higher rangeusually are practicable. This is also in part due to .the fact that thepermeation of the pressure-supplying gas into or through the body wallsis in general at a lower rate than for the cores alone.

Here again the polymerizing action may be further accelerated by thesimultaneous application of heat. 'I'his may beaccomplished by supplyingthe gas pressure medium in a heated condition or by providing heatwithin the chamber b in any convenient manner, electrically orotherwise, as by installing lights, coils or other heating orheat-supplying sourceh in or effective upon the chamber b, includingdiathermal or radiant heating means under automatic or other control.The temperature range may be generally similar as in connection withstation A2, from room temperature or thereabouts up to 300 F. or more,depending on the materials and bonding agents employed.

At the end of the treating period at station B2, which in general may beof a similar range of duration as at the station A2, the resultingintermediate products, consisting of the tube bodies 1 -Ill, havingtheir total bonding and impregnating agent polymerized so as to presentthe outer elements l in a hard dry and substantially smooth cleancondition at theirouter surfaces. are ready for' any followingoperation, such as phase C of the three-stage process. However for somepurposes the tubular products resulting at the end of operative phase Bmay be utilized without further treatment, particularly where in thenature of the use they are to be directly enclosed permanently withinsome othier means. Preferably, however, the tube bodies resulting fromthe treatment at station B2 are transferred by conveyor means orotherwise to a further Winding station such as indicated at C1. Hereagain, as in the case of stations A1 and B1, a plurality of windingunits or stations may be employed, so that a corresponding number of thetube bodies may be handled simultaneously.

At each such station C1 the tube bodies are again mounted or manipulatedin the manner of a mandrel and have applied over their straight-laidveener winding I0 an outer covering or protective finishing jacket asindicated at I3 in Figs. 1 and 4. 'I'his may be similar to that of Figs.6 and 7 of my earlier application Serial No. 453,931, comprising one ormore spiral wraps of thin wood stripping, lengthwise the strips and withalternate strips wound of opposite hand. Bonding and impregnating meansis applied, similarly as in connection with the procedure'at stations A1and B1. Following the application of the one or more spiral veneerlayers as atstation C1, two such layers being illustrated in Fig. 4, theresulting tubing products from the one or more stations'C1 ,latter afterapplication of an outer are cured and set. under a polymerizationexpediting treatment at a station C2. This latter may be the same in allrespects as at station B2, including a pressure-tight compartment c.Further detailed description in connection with station C2 accordinglyis unnecessary.

The end product following completion of the treating period at stationC2 of the third phase or stage C of the plural-phase process is asubstantially homogeneous tubing unit of substantial rigidity bothradially and axially and with hard and wear-resistant surfaces. improvedmethod of my present invention, including particularly the 'subjectionofthe cores, the intermediate elements or tube bodies, or the spiralcover, to the compressive and permeative action of a gaseous pressuremedium such as air, while maintaining a substantial positive pressuredifferential, internally as to the cores and externally as to the otherproduct stages, an extremely uniform end product results. Its outersurface is relatively smooth and clean, being free of adhering foreignmaterial such as frequently experienced under earlier practices. Byreason of the maintained air or other gas pressure differential, andespecially where the pressure medium is in a heated condition, thesubstantially direct contact thereof with the bonding and impregnatingagents materially facilitates their polymerization.

While I have illustrated and described provision for a positive pressuredifferential through a gaseous medium applied internally of the coreelements as at station A1, in certain instances, particularly with thelarger or thicker-walled cores the pressure may be applied externally,similarly as for stations B2 and C2. Conversely the pressure at thelatter stations may be utilized internally of the tubular structures. Instill other instances differential counter-acting positive pressures maybe applied simultaneously both inside and outside the hollow tubularstructures, such as thosey with comparatively thick walls.

My invention is not limited to the particular steps or means as hereinillustrated or described.

with the grain preferably y its scope being pointed I claim: 1. In themanufacture of wood tubing and the like, the process which includes thesteps of spirally winding wood veneer stripping to form out in thefollowing claims.

a hollow tubular core element, applying a polymerizable bonding agent tosuch winding, sealing the ends of said core element pressure-tight topresent its hollow interior as a closed chamber, supplying a gas mediumat above-atmospheric pressure to the sealed chamber of said core elementthereby creating a substantial positive pressure differential therein,maintaining such pressure differential during. medium at least partiallythrough the wall for a substantial portion of the polymerizing periodfor the particular bonding agent, thereafter winding one vor more veneerlayers onto the core element to provide a composite tubing body,applying a polymerizable bonding agent to and between the windings,venting the end-sealed interior chamber of the tubing body to notgreater ment and there subjecting it to a gaseous medium under pressureadequate to create a substantial positive pressure differentialexternally upon and into the body wall, and maintaining such pres'- suredifferential through at least an initial por- Under the permeation ofthe gas' non o: the pqlymerizing periodio'r the selected bonding agent.A2.; In the manufacture of wood tubing andthe like, the process whichcomprises spirally winding in alternating directions a plurality ofsuperposed wood strips and. applying a polymerizable bonding agentbetween each such winding, thereby to form a hollow tubular core,sealing the ends of the core pressure-tight to present its hollowinterior as a closed chamber, supplying gas under pressure' to said corechamber and maintaining the pressure therein until the bonding agent ispolymerized, wrapping upon the resulting hard dry core a surroundinglayer of wood veneer and interposing a similar bonding agent therefor,end sealing the resultant tubular body while affording communicationwith its hollow interior for atmospheric or negative pressure, placingsaid body in a closed pressure-tight chamber, and subjecting it to thepositive pressure of a gas medium uniformly'over its entire outercylindrical surface.

3. The process according to claim 2 including the further steps ofspirally winding a wood covering strip upon the resultant tubular bodywith an associated like bonding agent, and similarly end-sealing andcreating a positive pressure differential externally of and upontheresultant sealed hollow tubular body by a gas medium applied uniformlyexternally thereof.

4. The process of claim 1 including in combination therewith theapplication of heat while maintaining the positive internal pressuredifferential.

5. The. process of claim 1 including in combinationtberewith the heatingof the pressuresupplying gas medium.

6. The process of claim 1 including in combination therewith theapplication of heat while maintaining the external pressuredifferential.

1. In the manufacture ofwood tubing and the like, the process whichcomprises spirallywinding in alternating directions a plurality ofsuperposed wood strips and. applying a polymerizable bonding agentbetween each such winding, thereby to form a hollow tubular core,sealing the ends of lthe core pressure-'tight to present its hollowinterior as a closed chamber, supplying gas under pressure to said corechamber and maintaining the pressure therein untilthe bonding agent ispolymerized, wrapping upon the resulting hard dry core a surroundinglayer of wood'veneer and interposing a similar bonding agent therefor,end

f sealing the resultant tubular body while aording mospheric or negativepressure,

communication with its hollow interior for atplacing said body in aclosed pressure-tight chamber, and subjecting it to the positivepressure of a gas medium uniformly over its entire outer, cylindricalsurface, spirally winding a wood covering strip upon tneresultanttubular body with an associated like bonding agent. similarlyend-sealing and creating a positive pressure differential externally ofand upon the resultant sealed hollow tubular body by a gas mediumapplied uniformly externally thereof, and simultaneously subjecting thetubular structure to heat during any or each of the-periods of pressureapplication thereto.

PAUL R. GOLDMAN.

